Electrode for an Ignition Device

ABSTRACT

An electrode for an ignition device is made from a dilute nickel alloy which has improved resistance to high temperature oxidation, sulfidation, corrosive wear, deformation and fracture and includes at least 90% by weight of nickel; zirconium; boron and at least one element from the group consisting of aluminum, magnesium, silicon, chromium, titanium and manganese. The weight ratio of Zr/B may range from about 0.5 to 150, and may include amounts of, by weight of the alloy, 0.05-0.5% zirconium and 0.001-0.01% boron. The oxidation resistance of the alloy may also be improved by the addition of hafnium to the alloy in an amount that is comparable to the amount of zirconium, which may include an amount of, by weight of the alloy, 0.005-0.2% hafnium. Electrodes of dilute nickel alloys which include aluminum and silicon, as well as those which include chromium, silicon, manganese and titanium, are particularly useful as spark plug electrodes. These electrode alloys of the may also include at least one of cobalt, niobium, vanadium, molybdenum, tungsten, copper, iron, carbon, calcium, phosphorus or sulfur as trace elements, generally with specified maximum amounts. The ignition device may be a spark plug which includes a ceramic insulator, a conductive shell, center electrode and ground electrode. The center electrode, ground electrode, or both, may be made from the dilute nickel alloy of the invention. These electrodes may also include a core with thermal conductivity greater than that of the dilute nickel alloy, such as copper or silver or their alloys.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention relates to a high performance electrode made from a dilutenickel alloy containing alloying additions of zirconium and boron thatis temperature, oxidation, sulfidation and fracture resistant and, moreparticularly, toward an electrode for an ignition device, such as aspark plug for an internal combustion engine, furnace, or the like.

2. Related Art

A spark plug is a spark ignition device that extends into the combustionchamber of an internal combustion engine and produces a spark to ignitea mixture of air and fuel. Recent developments in engine technology areresulting in higher operating temperatures to achieve improved engineefficiency. These higher operating temperatures, however, are pushingthe spark plug electrodes to the very limits of their materialcapabilities. Presently, Ni-based nickel-iron-chromium alloys specifiedunder UNS N06600, such as those sold under the trade names Inconel 600®,Nicrofer 7615®, and Ferrochronin 600®, as well as various dilute nickelalloys, are in widespread use as spark plug electrode materials. Dilutenickel alloys are high nickel alloys, having nickel contents that aregenerally greater than 90% by weight of the alloy, with small amounts ofvarying alloying elements, such as silicon, aluminum, yttrium, chromium,titanium, cobalt, tungsten, molybdenum, niobium, vanadium, copper,calcium, manganese and the like, to improve the high temperatureproperties over that of pure nickel, including enhanced resistance tohigh temperature oxidation, sulfidation and associated corrosive wear,as well as deformation, cracking and fracture associated with cyclicthermo-mechanical stresses resulting from operation of these devices.

As is well known, the resistance to high temperature oxidation of thesedilute nickel alloys decreases as their operating temperature increases.Since combustion environments are highly oxidizing, corrosive wearincluding deformation and fracture caused by high temperature oxidationand sulfidation can result and is particularly exacerbated at thehighest operating temperatures. At the upper limits of operatingtemperature (e.g., 1400° F.), tensile, creep rupture and fatiguestrength also have been observed to decrease significantly which canresult in deformation, cracking and fracture of the electrodes.Depending on the electrode design, specific operating conditions andother factors, these high temperature phenomena may contributeindividually and collectively to undesirable growth of the spark pluggap and diminished performance of the ignition device and associatedengine. In extreme cases, failure of the electrode, ignition device andassociated engine can result from electrode deformation and fractureresulting from these high temperature phenomena. These failure modes andeffects can be particularly problematic in competitive applications,such as racing engines.

Accordingly, there is a need for high performance electrodes made fromdilute nickel alloys having improved resistance to high temperatureoxidation, sulfidation and related corrosive wear, as well as improvedhigh temperature tensile, creep rupture and fatigue strength andresistance to cracking and fracture.

SUMMARY OF THE INVENTION

In one aspect, the present invention includes an electrode for anignition device having improved resistance to high temperatureoxidation, sulfidation and related corrosive wear, as well as improvedhigh temperature tensile, creep rupture and fatigue strength andresistance to cracking and fracture which is formed from a dilute nickelalloy which includes at least 90% by weight of nickel; zirconium; boronand at least one element from the group consisting of aluminum,magnesium, silicon, chromium, titanium and manganese. The aluminum,silicon, chromium, titanium and manganese as diluent alloy elements maybe added in any combination and relative amounts, including all sixelements. The addition of zirconium and boron has been observed to havea synergistic effect on the improvement in properties noted in thesealloys as compared to the improvements resulting from the addition ofeither of these elements separately. The zirconium and boron willgenerally be present in a weight ratio of Zr/B of about 5 to 150, andmore particularly about 50 to 100, and most particularly about 70 to 80.While zirconium and boron may be present in any amounts consistent withthe requirements of the electrode alloy, it is believed that zirconiumin an amount of about 2.74% by weight or less and boron in an amount ofabout 3.50% by weight or less are generally believed to be the preferredupper limits for these constituents. It is also believed to be preferredthat the amount of zirconium be greater than the amount of boron. Indilute nickel alloys which include as diluent elements a combination ofaluminum and silicon; aluminum, silicon and yttrium; and chromium,silicon, manganese and titanium, the use of zirconium in the range of0.005-0.5% by weight of the alloy and boron in the range of 0.001-0.01%by weight of the alloy is particularly useful.

In another aspect, the dilute nickel electrodes of the invention mayalso include a rare earth alloying addition to enhance the oxidationresistance, including at least one rare earth element from the groupconsisting of yttrium, lanthanum, cerium and neodymium. In anotheraspect, to further improve the oxidation resistance, electrodes of theinvention may also include hafnium.

In yet another aspect, the dilute nickel electrodes of the invention mayalso include trace elements including at least one of cobalt, niobium,vanadium, molybdenum, tungsten, copper, iron, carbon, calcium,phosphorus or sulfur.

In yet another aspect, the dilute nickel electrodes of the invention mayinclude silicon and aluminum as diluent alloy elements. An example of adilute nickel electrode of the invention having silicon and aluminum asdiluent alloying elements is an alloy that includes, by weight of saidalloy: 1.0-1.5% aluminum; 1.0-1.5% silicon; 0.005-0.5% zirconium;0.001-0.01% boron and the balance substantially Ni. More particularly, adilute nickel electrode of the invention having silicon and aluminum asdiluent alloying elements is an alloy that includes 1.0-1.5% aluminum;1.0-1.5% silicon; 0.005-0.5% zirconium; 0.001-0.01% boron; 0.1-0.2%yttrium and the balance Ni and trace elements. Even more particularly, adilute nickel electrode of the invention having silicon and aluminum asdiluent alloying elements is an alloy that includes 1.0-1.5% aluminum;1.0-1.5% silicon; 0.005-0.5% zirconium; 0.001-0.01% boron; 0.1-0.2%yttrium, 0.005-0.2% hafnium and the balance Ni and trace elements.

In yet another aspect, dilute nickel electrodes of the invention mayinclude chromium, silicon, manganese and titanium as diluent alloyelements. An example of a dilute nickel electrode of the inventionhaving chromium, silicon, manganese and titanium as diluent alloyingelements is an alloy that includes, by weight of said alloy: 1.65-1.90%chromium; 0.35-0.55% silicon; 1.80-2.10% manganese, 0.20-0.40% titanium,0.005-0.5% zirconium; 0.001-0.01% boron and the balance substantiallyNi. More particularly, a dilute nickel electrode of the invention havingchromium, silicon, manganese and titanium as diluent alloying elementsis an alloy that includes 1.65-1.90% chromium; 0.35-0.55% silicon;1.80-2.10% manganese, 0.20-0.40% titanium, 0.005-0.5% zirconium;0.001-0.01% boron, 0.005-0.2% hafnium and the balance Ni and traceelements.

In yet another aspect, the ignition device is a spark plug having agenerally annular ceramic insulator; a conductive shell surrounding atleast a portion of the ceramic insulator; a center electrode disposed inthe ceramic insulator having a terminal end and a sparking end with acenter electrode sparking surface; and a ground electrode operativelyattached to the shell having a ground electrode sparking surface locatedproximate said center electrode sparking surface, said center electrodesparking surface and said ground electrode sparking surface defining aspark gap therebetween; wherein at least one of said center electrode orsaid ground electrode is an electrode of the invention.

The spark plug may also have a sparking tip attached to at least one ofthe center electrode or the ground electrode, wherein the sparking tipincludes one of gold, a gold alloy, a platinum group metal or a tungstenalloy. Platinum group metal sparking tips may include at least oneelement selected from the group consisting of platinum, iridium,rhodium, palladium, ruthenium and rhenium, including alloys thereof inany combination. The platinum group metal may also include at least oneelement from the group consisting of nickel, chromium, iron, manganese,copper, aluminum, cobalt, tungsten, yttrium, zirconium, hafnium,lanthanum, cerium and neodymium as an alloying addition.

In yet another aspect, the spark plug may have the center electrodeoperable with one of a positive polarity or an negative polarity and theground electrode operable at a ground potential.

The subject alloy and spark plug including an electrode made from thealloy overcomes certain disadvantages and shortcomings existing in priorart spark plugs and alloys to provide a dilute nickel alloy materialexhibiting the improved resistance to high temperatureoxidation/sulfidation, corrosion, deformation and fracture.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other features and advantages of the present invention willbecome more readily appreciated when considered in connection with thefollowing detailed description and appended drawings, wherein:

FIG. 1 is a partial cross-sectional view of an exemplary spark plugincluding shell and center electrodes manufactured from a Ni-basednickel-iron-chromium alloy according to the invention.

FIG. 2 is a cross-sectional view of region 2 of FIG. 1;

FIG. 3 is a cross-sectional view of region 3 illustrating an alternateelectrode configuration to that shown in FIG. 1 having thermallyconductive cores;

FIG. 4 is a partial cross-sectional view of an exemplary spark plugincluding shell and center electrodes manufactured from a Ni-basednickel-iron-chromium alloy according to the invention having a hightemperature sparking tip;

FIG. 5 is a cross-sectional view of region 5 of FIG. 4; and

FIG. 6 is a cross-sectional view of region 6 of FIG. 4 illustrating analternate electrode configuration to that shown in FIG. 4 havingthermally conductive cores.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIGS. 1-6, the present invention is an electrode for anignition device 5 used for igniting a fuel/air mixture. The electrodemay be used in any suitable ignition device 5, including variousconfigurations of spark plugs, glow plugs, igniters and the like, but isparticularly adapted for use in various spark plug electrodeconfigurations. The electrodes of an ignition device such as a sparkplug are essential to the function of the device. In spark ignitiondevices, such as spark plugs, the alloys used for the electrodes areexposed to the most extreme temperature, pressure, chemical corrosionand physical erosion conditions experienced by the device. These includeexposure of the electrode alloys to numerous high temperature chemicalreactant species associated with the combustion process which promoteoxidation, sulfidation and other corrosion processes, as well asreaction of the plasma associated with the spark kernel and flame frontwhich promote erosion of the spark surface of the electrode. Theelectrodes are also subject to thermo-mechanical stresses associatedwith the cyclic exposure to extreme temperatures, particularly to theextent corrosion processes form corrosion products on the electrodesurfaces having different physical and mechanical properties, such ascoefficients of thermal expansion, than the electrode alloy. Also, wherenoble metal spark tips are mechanically deformed, welded or otherwiseattached to the electrode ends as sparking surfaces, there areadditional cyclic thermo-mechanical stresses associated with themismatch in the thermal expansion coefficients of the noble metal tipand the electrode materials which can result in various high temperaturecreep, deformation, cracking and fracture phenomena, resulting infailure of the noble metal tips and electrodes. All of these representprocesses by which the properties of the electrodes may be degraded,particularly they can result in changes in the spark gap and thus theformation, location, shape, duration and other characteristics of thespark, which in turn affects the combustion characteristics of thefuel/air mixture and performance characteristics of the engine. Thepresent invention has improved resistance to these degradation processesover that of commonly used dilute nickel alloys that are frequently usedas center and ground electrode materials for spark plugs.

Referring to FIGS. 1-3, a spark plug having electrodes in accordancewith the subject invention is generally shown at 10. The spark plug 10includes a generally annular ceramic insulator, generally indicated at12, which includes aluminum oxide or another suitable electricallyinsulating material having a specified dielectric strength, highmechanical strength, high thermal conductivity, and excellent resistanceto thermal shock. The insulator 12 may be press molded from a ceramicpowder in a green state and then sintered at a high temperaturesufficient to densify and vitrify the ceramic powder. The insulator 12has an outer surface which may include a partially exposed upper portion14 to which a rubber or other insulating spark plug boot (not shown)surrounds and grips to electrically isolate an electrical connection ofthe terminal end 20 of the spark plug with an ignition wire and system(not shown). The exposed mast portion 14 may include a series of ribs 16or other surface glazing or features to provide added protection againstspark or secondary voltage flash-over and to improve the gripping actionof the mast portion with the spark plug boot. The insulator 12 is ofgenerally tubular or annular construction, including a central passage18 extending longitudinally between an upper terminal end 20 and a lowercore nose end 22. The central passage 18 generally has a varyingcross-sectional area, generally greatest at or adjacent the terminal end20 and smallest at or adjacent the core nose end 22.

An electrically conductive metal shell is generally indicated at 24.Metal shell 24 may be made from any suitable metal, including variouscoated and uncoated steel alloys. The shell 24 has a generally annularinterior surface which surrounds and is adapted for sealing engagementwith the exterior surface of the mid and lower portions of the insulator12 and includes at least one attached ground electrode 26. While groundelectrode 26 is depicted in a commonly used single L-shaped style, itwill be appreciated that multiple ground electrodes of straight, bent,annular, trochoidal and other configurations can be substituteddepending upon the intended application for the spark plug 10, includingtwo, three and four electrode configurations, and those where theelectrodes are joined together by annular rings and other structuresused to achieve particular sparking surface configurations. The groundelectrode 26 has one or more ground electrode sparking surface 15, on asparking end 17 proximate to and partially bounding a spark gap 54located between ground electrode 26 and a center electrode 48 which alsohas an associated center electrode sparking surface 51. The spark gap 54may constitute an end gap, side gap or surface gap, or combinationsthereof, depending on the relative orientation of the electrodes andtheir respective sparking ends and surfaces. Ground electrode sparkingsurface 15 and center electrode sparking surface 51 may each have anysuitable cross-sectional shape, including round, rectangular, square andother shapes, and these shapes may be different.

The shell 24 is generally tubular or annular in its body section andincludes an internal lower compression flange 28 adapted to bear inpressing contact against a small mating lower shoulder 11 of theinsulator 12. The shell 24 generally also includes an upper compressionflange 30, which is crimped or formed over during the assembly operationto bear on a large upper shoulder 13 of the insulator 12. Shell may alsoinclude a deformable zone 32 which is designed and adapted to collapseaxially and radially inwardly in response to heating of deformable zone32 and associated application of an overwhelming axial compressive forceduring or subsequent to the deformation of upper compression flange 30in order to hold shell 34 in a fixed axial position with respect toinsulator 12 and form a gas tight radial seal between insulator 12 andshell 24. Gaskets, cement, or other sealing compounds can also beinterposed between insulator 12 and shell 24 to perfect a gas-tight sealand to improve the structural integrity of assembled spark plug 10.

Shell 24 may be provided with a tool receiving hexagon 34 or otherfeature for removal and installation of the spark plug in a combustionchamber opening. The feature size will preferably conform with anindustry standard tool size of this type for the related application. Ofcourse, some applications may call for a tool receiving interface otherthan a hexagon, such as slots to receive a spanner wrench, or otherfeatures such as are known in racing spark plug and other applications.A threaded section 36 is formed on the lower portion of metal shell 24,immediately below a sealing seat 38. The sealing seat 38 may be pairedwith a gasket (not shown) to provide a suitable interface against whichthe spark plug 10 seats and provides a hot gas seal of the space betweenthe outer surface of the shell 24 and the threaded bore in thecombustion chamber opening. Alternately, the sealing seat 38 may bedesigned as a tapered seat located along the lower portion of the shell24 to provide a close tolerance and a self-sealing installation in acylinder head which is also designed with a mating taper for this styleof spark plug seat.

An electrically conductive terminal stud 40 is partially disposed in thecentral passage 18 of the insulator 12 and extends longitudinally froman exposed top post 39 to a bottom end 41 embedded partway down thecentral passage 18. Top post 39 connects to an ignition wire (not shown)which is typically embedded in an electrically isolating boot asdescribed herein and receives timed discharges of high voltageelectricity required to fire the spark plug 10 by generating a spark inspark gap 54.

Bottom end 41 of the terminal stud 40 is embedded within a conductiveglass seal 42, forming the top layer of a composite three layersuppressor-seal pack 43. Conductive glass seal 42 functions to seal thebottom end of terminal stud 40 and electrically connect it to a resistorlayer 44. This resistor layer 44, which comprises the center layer ofthe three-layer suppressor-seal pack, can be made from any suitablecomposition known to reduce electromagnetic interference (“EMI”).Depending upon the recommended installation and the type of ignitionsystem used, such resistor layers 44 may be designed to function as amore traditional resistor-suppressor or, in the alternative, as aninductive-suppressor, or a combination thereof. Immediately below theresistor layer 44, another conductive glass seal 46 establishes thebottom or lower layer of the suppressor-seal pack 43 and electricallyconnects terminal stud 40 and suppressor-seal pack 43 to the centerelectrode 48. Top layer 42 and bottom layer 46 may be made from the sameconductive material or different conductive materials. Many otherconfigurations of glass and other seals and EMI suppressors arewell-known and may also be used in accordance with the invention.Accordingly, electrical charge from the ignition system travels throughthe bottom end of the terminal stud 40 to the top layer conductive glassseal 42, through the resistor layer 44, and into the lower conductiveglass seal layer 46.

Conductive center electrode 48 is partially disposed in the centralpassage 18 and extends longitudinally from its head 49 which is encasedin the lower glass seal layer 46 to its sparking end 50 proximate groundelectrode 26. Center electrode sparking surface 51 is located onsparking end 50 and is located opposite ground electrode sparkingsurface 15, thereby forming a spark gap 54 in the space between them.The suppressor-seal pack electrically interconnects terminal stud 40 andcenter electrode 48, while simultaneously sealing the central passage 18from combustion gas leakage and also suppressing radio frequency noiseemissions from the spark plug 10 during its operation. As shown, centerelectrode 48 is preferably a one-piece structure extending continuouslyand uninterrupted between its head and its sparking end 50. It will bereadily understood and within the scope of this invention that thepolarity of the center electrode 48 during operation of the spark plug10 may be either positive or negative such that the center electrode 48has a potential which is either higher or lower than ground potential.

This is a representative construction of spark plug 10, but it will bereadily appreciated that other spark plug 10 or ignition device 5constructions using insulator 12, shell 24 and electrodes 26 and 48 arepossible in accordance with the present invention.

Preferably both, but at least one, of the center 48 and shell 26electrodes are fabricated from a dilute nickel alloy which has beenspecially formulated to have improved resistance to the degradationprocesses described above over that of similar alloy formulations whichdo not incorporate these improvements. Specifically, the improved alloyformulations incorporate particular amounts of zirconium and boron tothe alloy formulation which have been observed to produce improvedresistance to the degradation processes described herein over similaralloy formulations which do not include these alloying additions.Generally, the small amounts of zirconium and boron added aresubstituted for an equivalent amount of nickel to produce thisimprovement. The electrodes of the invention includesolution-strengthened dilute nickel alloys comprising at least 90% byweight of nickel; zirconium; boron and at least one element from thegroup consisting of aluminum, silicon, chromium, titanium and manganese.Based on similar improvements observed by Applicants insolution-strengthened Ni-based nickel-chromium-iron alloys which alsocontain zirconium and boron as described herein, namely U.S. patentapplication Ser. No. ______ (Attorney Docket IG-40555; 710240-2763)filed on even date herewith which is hereby incorporated by reference inits entirety, it is believed that this invention extends also to sparkplug electrodes made from other solution-strengthened Ni-based alloys,including those comprising zirconium, boron, at least one othersolution-strengthening constituent and at least 50% nickel. These alloyswould include any suitable solution-strengthening constituent, includingthose described herein. Alloy constituent percentages given herein arepercentages by weight of the alloy unless otherwise stated.

The zirconium and boron are generally included in amounts such that theweight ratio of Zr/B ranges from about 5 to 150. However, a morepreferred range of this ratio is about 50 to 100, and a most preferredrange being about 70 to 80. While zirconium and boron may present in anyamounts consistent with the other requirements of the electrode alloy,it is believed that zirconium in an amount of about 2.74% by weight orless and boron in an amount of about 3.50% by weight or less are thepreferred upper limits for these constituents. It is also believed to bepreferred that the amount of zirconium be greater than the amount ofboron. In solution-strengthened dilute nickel alloys generally, the useof zirconium in the range of 0.005-0.5% by weight of the alloy and boronin the range of 0.001-0.01%, by weight of the alloy is believed to beparticularly useful. In the alloy compositions described above whichinclude at least one element from the group consisting of aluminum,silicon, chromium, titanium and manganese, the use of zirconium in therange of 0.005-0.15% by weight of the alloy and boron in the range of0.001-0.01% by weight of the alloy is known to be particularly useful.Boron and zirconium are known as grain boundary strengtheners. Theysegregate to the grain boundaries and serve to stabilize them increasinggrain boundary strength and ductility, retarding grain boundarydiffusion and sliding and delaying intergranular cracking caused beenvironmental and mechanical factors under the operating conditions ofthe electrodes, thereby inhibiting high temperature grain growth andenhancing the resistance of these alloys to high temperature creep,deformation, environmental cracking and various fracture phenomena, suchas stress rupture. The performance improvements associated with theaddition of zirconium and boron are synergistic, that is they aregreater than the improvements that result when either zirconium or boronare added to these alloys separately.

As a further improvement to the degradation resistance of these alloys,particularly by what is believed to be improvement of the hightemperature oxidation and sulfidation resistance, the electrode alloymaterial compositions described above may also include hafnium. Theamount of hafnium may range from about 0.005-0.2%. The amount of thehafnium may be generally comparable to the amount of the zirconium, butthis is not essential to the invention. By enhancing the resistance tooxidation and sulfidation, the alloy has improved resistance to variouscracking and oxide scale spalling phenomena associated with thecoefficient of thermal expansion mismatch between those of these speciesand that of the alloy and thermo-mechanical stresses that tend topropagate such cracks.

The dilute nickel alloys of the invention include at least 90% nickel.The nickel is diluted by one or more diluent elements as an alloyingaddition. Most generally, these alloys may include as an alloyingaddition at least one metal selected from the group consisting aluminum,silicon, chromium, titanium and manganese. More particularly, they mayinclude two of these elements in any combination. Even moreparticularly, they may include three of these elements in anycombination. Even more particularly, they may include four of theseelements in any combination. Even more particularly, they may includefive of these elements in any combination, and most particularly, theymay include all six of these elements.

As a further improvement to the degradation resistance of these alloys,particularly by improvement of the high temperature oxidationresistance, the electrode alloy material compositions described abovemay also include at least one rare earth element as an alloyingaddition. For purposes of this application, the definition of rare earthelements also includes yttrium and hafnium, as described above, whichare reactive transition metals but which produce improvements to thesesolution-strengthened dilute nickel alloys similar to those produced bythe addition of the rare earth element alloying additions. Morespecifically, the rare earth elements will include at least one elementselected from the group consisting of yttrium, hafnium, lanthanum,cerium, and neodymium. However, any combination of rare earth elementalloying additions is comprehended within the scope of this invention.Also, more specifically, the compositional range of all rare earthelement alloying additions is preferably limited to about 0.1-0.2% byweight of the alloy. In the cases where hafnium is selected, its amountsmay range independently of the other rare earth constituents in themanner described above; however, it is preferred that the total of allrare earth element constituents be about 0.1-0.2% by weight of thealloy.

The electrode alloy material may also include trace amounts of otherelements. These trace elements may be incidental impurity elements.Typically incidental impurities are associated with the processes usedto manufacture the primary alloy constituent materials or the processesused to form the electrode alloy. However, if the purity of the otherelectrode constituents and the manufacturing process is controlled,these trace elements need not be incidental and their presence orabsence and relative amounts may be controlled. The trace elements mayinclude iron, calcium, cobalt, niobium, vanadium, tungsten, molybdenum,copper, carbon, phosphorus and sulfur in any combination. The electrodealloy material of the invention will typically include at least one ofthese elements, with the total number of them typically associated withthe sources and manufacturing methods used to produce the constituentsnoted. Some of these elements, including iron, cobalt, niobium,tungsten, vanadium, molybdenum, copper and carbon may have a neutral toslightly positive influence on the high temperature properties describedherein, while others may have a slightly negative effect on them,including calcium, phosphorus and sulfur. To the extent these elementsare present in the alloy, regardless of whether they have a positive ornegative effect on its high temperature properties, it is preferred tolimits their amounts as follows, by weight of the alloy: cobalt 0.05%max, niobium 0.01% max, vanadium 0.01 max., molybdenum 0.01% max,tungsten 0.01 max., copper 0.05% max, carbon 0.01% max, lead 0.005% max,phosphorus 0.005% max and sulfur 0.005% max.

In an exemplary embodiment of an alloy of the invention having twodiluent constituents, the elements may include aluminum and silicon.More particularly, the alloy includes: 1.0-1.5% aluminum; 1.0-1.5%silicon; 0.005-0.5%, zirconium; 0.001-0.01% boron and the balancesubstantially nickel. Even more particularly, for improved resistance tooxidation this alloy may include: 1.0-1.5% aluminum; 1.0-1.5% silicon;0.005-0.5% zirconium; 0.001-0.01% boron; 0.1-0.2% yttrium and thebalance Ni and trace elements. Still even more particularly, for evenmore resistance to oxidation, this alloy may include: 1.0-1.5% aluminum;1.0-1.5% silicon; 0.005-0.5% zirconium; 0.001-0.01% boron; 0.1-0.2%yttrium, 0.005-0.2% hafnium and the balance Ni and trace elements.

In another exemplary embodiment of an alloy of the invention having fourdiluent constituents, the elements may include chromium, silicon,manganese and titanium. More particularly, the alloy includes:1.65-1.90% chromium; 0.35-0.55% silicon; 1.80-2.10% manganese,0.20-0.40% titanium, 0.005-0.015% zirconium; 0.001-0.01% boron and thebalance substantially Ni. Even more particularly, for improvedresistance to oxidation this alloy may include: 1.65-1.90% chromium;0.35-0.55% silicon; 1.80-2.10% manganese, 0.20-0.40% titanium,0.005-0.015% zirconium; 0.001-0.01% boron, 0.005-0.2% hafnium and thebalance Ni and trace elements.

Spark plug ground electrodes 26 and center electrodes 48 made from thedilute nickel alloy material composition as described have improvedresistance to oxidation, sulfidation and associated corrosive wear, aswell as improved resistance to cracking and fracture associated withthermo-mechanical stresses in the extremely adverse environment of thecombustion chamber of an internal combustion engine.

As shown in FIG. 3, in an alternate electrode configuration, either oneor both of the ground electrode 26 and center electrode 48 can beprovided with thermally conductive cores 27, 49, respectively, made frommaterial of high thermal conductivity (e.g., ≧250 W/M*°K) such as copperor silver or various alloys of either of them. Highly thermallyconductive cores serve as heat sinks and help to draw heat away from thespark gap 54 region, thereby lowering the operating temperature of theelectrodes in this region and further improving their performance andresistance to the degradation processes described herein.

As shown in FIGS. 4-6, the spark plug 10 may also incorporate on thesparking ends of either or both of the ground electrode 26 or centerelectrode 48 a firing tip 62,52, respectively, of a different hightemperature material that has either improved spark performance orresistance to the degradation processes described, or both of them. Thismay include all manner of noble and non-noble metal firing tips. Centerelectrode 48 firing tip 52 is located on sparking end 50 of thiselectrode and has a sparking surface 51′. Ground electrode 26 firing tip62 is located on sparking end 17 of this electrode and has a sparkingsurface 15′. Firing tips 52,62, when used, include respective sparkingsurfaces 51′, 15′ for the emission of electrons across the spark gap 54.Firing tip 52 for the center electrode 48 and firing tip 62 for groundelectrode 26 can each be made and joined according to any of a number ofknown techniques, including the formation and attachment, or thereverse, of various pad-like, wire-like or rivet-like firing tips byvarious combinations of resistance welding, laser welding, orcombinations thereof. Firing tips 52, 62 may be made from gold or goldalloys, including Au—Pd alloys, such as Au-40Pd (in weight percent)alloys. Firing tips 52,62 also may be made from any of the known puremetals or alloys of the platinum group metals, including: platinum,iridium, rhodium, palladium, ruthenium and rhenium, and various alloycombinations thereof in any combination. For purposes of thisapplication, rhenium is also included within the definition of platinumgroup metals based on its high melting point and other high temperaturecharacteristics similar to those of certain of the platinum groupmetals. Additional alloying elements for use in firing tips 52,62 mayinclude, but are not limited to, nickel, chromium, iron, manganese,copper, aluminum, cobalt, tungsten, zirconium, and rare earth elementsincluding yttrium, lanthanum, cerium, and neodymium. In fact, anymaterial that provides suitable spark erosion corrosion performance inthe combustion environment may be suitable for use as firing tips 52,62.Firing tips 52,62 may also be made from various tungsten alloys,including W—Ni, W—Cu and W—Ni—Cu alloys.

The subject dilute nickel electrode materials are also beneficial when afiring tip 52,62 or other feature is welded to an electrode body madethereof. It provides improved strength and durability and resistance tofracture of the weld at high temperatures. While the subject dilutenickel electrode material has been described for use in the particularapplication of a shell 26 and/or center 48 electrode for a spark plug10, it will be appreciated that other uses and applications for thesubject alloy to electrodes for other ignition devices will be readilyappreciated by those of skill in the art due to the invented material'ssuperior resistance to high temperature oxidation and sulfidation, hightemperature mechanical strength, and improvements in resistance tocracking and fracture of weld attachments due to thermo-mechanicallyinduced stresses, particularly weld attachments associated with variousfiring tip configurations.

Obviously, many modifications and variations of the present inventionare possible in light of the above teachings. It is, therefore, to beunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise than as specifically described.

1. An electrode for an ignition device, said electrode formed from analloy comprising: at least 90% by weight of nickel; zirconium; boron andat least one element from the group consisting of aluminum, silicon,chromium, titanium and manganese.
 2. The electrode of claim 1, furthercomprising hafnium.
 3. The electrode of claim 1, wherein said at leastone element is selected to include silicon and aluminum.
 4. Theelectrode of claim 3, comprising, by weight of said alloy: 1.0-1.5%aluminum; 1.0-1.5% silicon; 0.005-0.5% zirconium; 0.001-0.01% boron andthe balance substantially Ni.
 5. The electrode of claim 3, furthercomprising at least one rare earth element from the group consisting ofyttrium, hafnium, lanthanum, cerium and neodymium.
 6. The electrode ofclaim 5, comprising, by weight of said alloy: 1.0-1.5% aluminum;1.0-1.5% silicon; 0.005-0.5% zirconium; 0.001-0.01% boron; 0.1-0.2%yttrium and the balance Ni and trace elements.
 7. The electrode of claim5, wherein said at least one rare earth element is selected to includeyttrium and hafnium.
 8. The electrode of claim 7, comprising, by weightof said alloy: 1.0-1.5% aluminum; 1.0-1.5% silicon; 0.005-0.5%zirconium; 0.001-0.01% boron; 0.1-0.2% yttrium, 0.005-0.2% hafnium andthe balance Ni and trace elements.
 9. The electrode of claim 6, whereinsaid trace elements comprise at least one of cobalt, niobium, vanadium,molybdenum, tungsten, copper, iron, carbon, calcium, phosphorus orsulfur.
 10. The electrode of claim 8, wherein said trace elementscomprise at least one of cobalt, niobium, vanadium, molybdenum,tungsten, copper, iron, carbon, calcium, phosphorus or sulfur.
 11. Theelectrode of claim 1, wherein said at least one element is selected toinclude chromium, silicon, manganese and titanium.
 12. The electrode ofclaim 11, comprising, by weight of said alloy: 1.65-1.90% chromium;0.35-0.55% silicon; 1.80-2.10% manganese, 0.20-0.40% titanium,0.005-0.5% zirconium; 0.001-0.01% boron and the balance substantiallyNi.
 13. The electrode of claim 11, further comprising hafnium.
 14. Theelectrode of claim 13, comprising, by weight of said alloy: 1.65-1.90%chromium; 0.35-0.55% silicon; 1.80-2.10% manganese, 0.20-0.40% titanium,0.005-0.5% zirconium; 0.001-0.01% boron, 0.005-0.2 hafnium and thebalance Ni and trace elements.
 15. The electrode of claim 12, whereinsaid trace elements comprise at least one of cobalt, niobium, vanadium,molybdenum, tungsten, copper, iron, carbon, calcium, phosphorus orsulfur.
 16. The electrode of claim 14, wherein said trace elementscomprise at least one of cobalt, niobium, vanadium, molybdenum,tungsten, copper, iron, carbon, calcium, phosphorus or sulfur.
 17. Theelectrode of claim 1, wherein said ignition device is a spark plugfurther comprising: a generally annular ceramic insulator; a conductiveshell surrounding at least a portion of said ceramic insulator; a centerelectrode disposed in said ceramic insulator having a terminal end and asparking end with a center electrode sparking surface; and a groundelectrode operatively attached to said shell having a ground electrodesparking surface located proximate said center electrode sparkingsurface, said center electrode sparking surface and said groundelectrode sparking surface defining a spark gap therebetween; wherein atleast one of said center electrode or said ground electrode is saidelectrode.
 18. The electrode of claim 17, wherein said center electrodeis operable with one of a positive polarity or a negative polarity andthe ground electrode is operable at a ground potential.
 19. Theelectrode of claim 17, further comprising a sparking tip attached to atleast one of said center electrode or said ground electrode, whereinsaid sparking tip comprises one of gold, a gold alloy, a platinum groupmetal or a tungsten alloy.
 20. The electrode of claim 19, wherein saidplatinum group metal comprises at least one element selected from thegroup consisting of platinum, iridium, rhodium, palladium, ruthenium andrhenium.
 21. The electrode of claim 20, wherein said platinum groupmetal further comprises at least one element from the group consistingof nickel, chromium, iron, manganese, copper, aluminum, cobalt, yttrium,tungsten, zirconium, hafnium, lanthanum, cerium and neodymium.